Microbiological processes have been used by man throughout recorded history. Most societies, however, primitive, use a fermentation process to produce beverages containing ethanol. In addition, such compounds as acetic acid, acetone, n-butyl alcohol as well as formic, lactic, and propionoic acids are produced by microbiological processes. Materials of the type mentioned are important articles of commerce, both as such, and as a consequence of the derivatives and materials which can be produced therefrom.
Commonly, microbiological processes are carried out in batch processes in which a nutritive feed, in the case of wine, grape juice, is inoculated with the particular strain of microorganism selected, and the reaction is permitted to continue until the environment is for one reason or another no longer conductive to continuation of the reaction. Batch processes of the type described are slow, however, frequently produce erratic results, and they usually require large equipment.
Continuous processes, on the other hand, are noted for the uniformity of product which they are capable of producing, in addition to the speed with which they can be carried out. Furthermore, since continuous processes make high rates of production possible, smaller, normally less expensive equipment than in the case of batch processes may be employed to achieve the desired rate of production.
In the case of microbiological reactions, continuous processes may be carried out, for instance, in packed columns. Such equipment usually consists of cylindrical vessels filled with packing material such as beryl saddles, rasching rings, spheres and the like, the surface of which is innoculated by being exposed to the microorganism capable of carrying out the desired reaction. A nutrative feed is then introducted at one end of the column, allowed to proceed through the packing, and withdrawn at the other end in a continuous manner. A device of the type described, known as a "bioreactor", when operated under constant conditions of feed rates, temperatures, and the like, eventually results in separate and distinct colonies of microorganisms oriented in zones along its vertical height. For example, at the point in the column where the nutrative feed is introduced, it will be found that microorganisms in the vicinity will be of a type which are adapted to high concentrations of nutrients. Further along the column, organisms will be found which can thrive on a more dilute nutritive feed, in the presence of more product, while those still further along can operate with still less nutrients, and which are even better adapted to withstand high concentrations of the product produced by the bioreaction, for instance, high alcohol concentrations. The colonization of successive areas along the packed column with organisms uniquely adapted to the conditions at their location provides an unusually efficient reaction overall, since each zone of the column is populated by microorganisms best able to cope with the conditions existing at that point.
While bioreactors are theoretically uniquely suited to carrying out microbiological processes, they have an unfortunate tendency to clog eventually due to the build-up of the microorganisms and the debris associated therewith, on the packing material. Such a build-up eventually reduces the throughput of the column and changes the environment within the different zones. When plugging of the type described proceeds far enough, it becomes necessary to discontinue operation of the column and remove and clean the packing before reintroducing it so that the reaction can continue. Furthermore, after the packing has been cleaned and replaced, it is sometimes necessary to reinoculate it with the desired microorganism. However, even in those instances where this is not necessary, one finds that the packing particles are so thoroughly remixed that the stratification of specific colonies of microorganisms is destroyed. In either case, an appreciable period of time is required to re-establish the previous equalibrated stratification, resulting in lower productivity and higher costs.